Moon Anomaly

[pez1]

As I was leaving the office before dawn, I decided to grab a hand-held Moon shot since I had my camera with 420mm of lens on it, and there was the Moon. So, I ended up taking several frames, because of this anomaly. I noticed it through the viewfinder. WTH is it? Kind of looks like a shadow, to my eye. Sorry for the low-res...

 

[pez1]

I've taken many, many images of the Moon over the years, and this is the weirdest thing I've ever seen.